1. Field of the Invention
This invention relates generally to expandable intraluminal vascular grafts, generally referred to as stents, and more particularly concerns metal stents coated with a polymer capable of carrying and releasing therapeutic drugs.
2. Description of Related Art
Stents used to maintain patency of vessels in the body are typically implanted within a vessel in a contracted state, and are expanded when in place in the vessel to allow fluid to flow through the vessel and the stent. Such a stent can typically be moved along a guide wire previously placed in the vessel, and expanded by inflation of a balloon within the stent. Deflation of the balloon and removal of the guide wire leaves the stent in place in the vessel, locked in an expanded state. While stents are typically formed from biocompatible metals such as stainless steel, tantalum or gold, to provide sufficient strength to function as a stent, and with a minimal thickness so as to minimize blood flow blockage, such stents can cause complications such as thrombosis, and can cause neointimal hyperplasia, such as by inducement of smooth muscle cell proliferation at the site of implantation of the stent. Such stents typically also do not provide for the delivery of localized therapeutic pharmacological treatment of a blood vessel at the location being treated with the stent, which can be useful for overcoming such problems.
Polymeric materials capable of absorbing and releasing therapeutic drugs do not generally have sufficient strength to function as a stent to maintain luminal patency. It would therefore be desirable to form a stent of a combination of materials that provide sufficient radial strength to serve as a stent, and are capable of absorbing therapeutic drugs and releasing them at a predictable rate for an ascertainable period of time in a blood vessel. The present invention meets these needs.